One of the most important components of a computer is the magnetic disk drive. The hard drive includes magnetic disks and sliders where the magnetic head assembly including write and read heads are mounted, the suspension arms accommodating them, and an actuator arm, and the related controlling circuitry. When the magnetic disks rotate, air adjacent to the disk surface moves with them. This allows the sliders, i.e., the individual magnetic heads, to fly on an extremely thin cushion layer of air, generally referred to as an air bearing. When the slider flies on the air bearing, the actuator arm swings the suspension arm to place the magnetic head assembly over selected circular tracks on the rotating magnetic disk where signal fields are written and read by the write and read heads respectively. The write and read heads are connected to signal processing circuitry that operates according to a computer program to implement write and read functions.
As areal data density requirements push manufactures to produce ever smaller read and write heads, the need to control manufacturing with tighter tolerances increases dramatically. This is particularly true when the perpendicular recording design is introduced for magnetic disk drive production for the next generation high areal density data storage (>130 Gbit/in2) requirements. In a finished head, the distance of flare location of the write pole to the air bearing surface (ABS) is very important since it determines the performance of the write head. Unfortunately this parameter cannot be clearly defined at the wafer level since the air bearing surface has not yet been defined. The ABS is formed when the head build is finished and heads are sliced off from the wafer and after mechanical lapping. The mechanical lapping exposes both the read sensor at ABS and the distance of the write pole flare to ABS is then defined. Since the lapping process uses the location of the read sensor as a reference, the write pole flare location to ABS can be predicted as long as the flare can be referenced to the location of the read sensor during the wafer process, which is far upstream from the finished sliders. In modern manufacturing metrology, the rear edge of the read sensor is commonly used as a reference point since it remains in the finished head after lapping. Therefore, it is highly desirable for a metrology solution to identify the write pole flare location referenced to read sensor for performing write head flare feedback and process control at an early stage of the head build. This enables the performance prediction of the heads at an earlier stage before they are finished from the build.
The entire magnetic head is built through layers of thin films through deposition, photolithography, ion milling, plating steps, etc on the ceramic composite wafers. During the write head process for perpendicular recording, a write pole of a write head has a narrow, constant cross section that extends to a desired distance from the ABS by design. By design, at a desired distance from the ABS the write pole flares laterally outward. The point at which this flare initiates is called the flare point, and the location of the flare point is important to proper write head performance.
Unfortunately, the location of the flare point during manufacture is not stationary. It is susceptible to process variations, and it may move along the pole axis direction after certain process steps. For example, during an ion milling operation used to trim and form the write pole profile, the location of the flare point is affected and thus moved. While the distance from the flare location to ABS needs to be identified, the method to identify this distance during the wafer level is the key to accurately predict the final location of the flare point at head level.
Therefore, there is a strong felt need for a manufacturing method for accurately determining and controlling the flare point location during the manufacture of a write pole. Such a method would identify the write pole flare location using the read sensor rear edge as a reference. Such a method would preferably not incur significant additional cost or manufacturing complexity and would preferably be capable of being incorporated into existing manufacturing processes.